EPC monolayers at the oil/water interface

MOTTOLA, MILAGRO; PERILLO, MARÍA ANGÉLICA

Salto

Congreso; Latin American Crosstalk in Biophysics and physiology; 2015

Seccional Biofísica Uruguaya (SBF.uy), Sociedad Argentina de Biofísica (SAB), LAFeBS

Lipids, mainly from vegetable oils and dairy fat, have gained renewed interest as excipients in pharmaceutical formulations for the oral administration of hydrophobic drugs due to their capability to enhance drug?s bioavailability and to reduce the variability of plasma concentrations. Lipidic microemulsions are systems commonly used to encapsulate, maintain, and release molecules of pharmacological interest. In order to gain insights about interfaces within microemulsions at the molecular level1, by using a Langmuir interfacial trough, we have characterized, at different temperatures, monomolecular layers of egg L-α-phosphatidylcholine (EPC) at oil/water interfaces (O/W) where the upper phases differed in viscosity: Vaseline 80 SSU/water, Vaseline 80 SSU:n-heptane(1:1)/water, and n-heptane/water. Moreover, for the film preparation, two different techniques were assayed in order to make adsorbed (AM) or spread monolayers (SM)2. Since the AM were formed by adsorption of the lipid to the interface when the solution is spread over the upper phase, our first approach consisted on a detailed study about how the spreading distance from the Wilhelmy plate affected the molecules? diffusion at the O/W interface. In contrast, to form SM, the EPC solution was spread over an air-water interface to form a monolayer and then the oil was poured over it to obtain the O/W interface. Although the second method was easier to apply, similar results were obtained with both techniques. The apparent mean molecular areas (MMAap) of EPC measured at the O/W interface were higher than those exhibited in the air/water interface at the same lateral pressure. This expansion of EPC monolayer suggests that the alkane molecules from the upper phase insert between the hydrocarbon chains of the phospholipid and are not squeezed out even at the highest compressions achieved before the collapse point. References: [1] Thoma M, et al. JCIS. 162:340-349, 1994.[2] Solovyev A, et al. Energy & Fuels 20:1572-1578, 2006. Acknowledgements and Support: FONCyT, CONICET y SeCyT-UNC.